You and I are among the lucky. The neonatenous state of creativity and "childlike wonder" has a heavy genetic component.

You can temper that by "using your brain" doing puzzles, reading, learning a new language, etc. But, there is a limit to how much that helps. Mostly it's genetic.

Like Roy Batty, we weren't made to last. Our creator is a real bastard about getting an extension.

If you get into your late 60's and the window stays open, it probably won't ever close.

In some fields it's brutal. It's why physicists are "washed up" at 30-35. Typically they stop being creative enough to push the envelope. Exceptions like Einstein and Penrose are, well, exceptional.